Functional neuroimaging studies suggest that prefrontal cortex dysfunction is present in people with autism spectrum disorder (ASD). Near-infrared spectroscopy is a noninvasive optical tool for examining oxygenation and hemodynamic changes in the cerebral cortex by measuring changes in oxygenated hemoglobin.
Uratani et al Child Adolesc Psychiatry Ment Health (2019) 13:29 https://doi.org/10.1186/s13034-019-0289-9 RESEARCH ARTICLE Child and Adolescent Psychiatry and Mental Health Open Access Reduced prefrontal hemodynamic response in pediatric autism spectrum disorder measured with near‑infrared spectroscopy Mitsuhiro Uratani1, Toyosaku Ota2* , Junzo Iida3, Kosuke Okazaki2, Kazuhiko Yamamuro2, Yoko Nakanishi2, Naoko Kishimoto2 and Toshifumi Kishimoto2 Abstract Background: Functional neuroimaging studies suggest that prefrontal cortex dysfunction is present in people with autism spectrum disorder (ASD) Near-infrared spectroscopy is a noninvasive optical tool for examining oxygenation and hemodynamic changes in the cerebral cortex by measuring changes in oxygenated hemoglobin Methods: Twelve drug-naïve male participants, aged 7–15 years and diagnosed with ASD according to DSM-5 criteria, and 12 age- and intelligence quotient (IQ)-matched healthy control males participated in the present study after giving informed consent Relative concentrations of oxyhemoglobin were measured with frontal probes every 0.1 s during the Stroop color-word task, using 24-channel near-infrared spectroscopy Results: Oxyhemoglobin changes during the Stroop color-word task in the ASD group were significantly smaller than those in the control group at channels 12 and 13, located over the dorsolateral prefrontal cortex (FDR-corrected P: 0.0021–0.0063) Conclusion: The results suggest that male children with ASD have reduced prefrontal hemodynamic responses, measured with near-infrared spectroscopy Keywords: Pediatric autism spectrum disorder, Near-infrared spectroscopy, Prefrontal hemodynamic response, Attention, Executive function Background Autism spectrum disorder (ASD) is a neurodevelopmental disorder, characterized by impairments in social and communicative functioning and the presence of restricted interests and repetitive behaviors [1] Studies using neuropsychological measures have revealed an association between ASD and inattention ASD can be characterized by a short attention span, and impulsivity and inattention symptoms are common [2] Furthermore, individuals with ASD are typically impaired on neurocognitive measures of sustained and selective attention [3] There is evidence for fronto-striatal, parietal, and *Correspondence: toyosaku@naramed‑u.ac.jp Department of Psychiatry, Nara Medical University, 840 Shijyo‑cho, Kashihara, Nara 634‑8522, Japan Full list of author information is available at the end of the article cerebellar abnormalities in ASD during selective and flexible attention [4, 5] In addition to attentional difficulties, many studies have indicated that individuals with ASD exhibit impairments of executive function [6, 7] A wealth of data indicates that the prefrontal cortex plays a major role in executive function Multi-channel near-infrared spectroscopy (NIRS) enables the noninvasive detection of neural activity near the surface of the brain using near-infrared light [8, 9] NIRS measures alterations in oxygenated hemoglobin (oxy-Hb) and deoxygenated hemoglobin (deoxy-Hb) concentrations in micro-blood vessels on the brain surface Local increases in the concentration of oxy-Hb and decreases in the concentration of deoxy-Hb are indicators of cortical activity [8, 10] In addition, changes in the concentration of oxy-Hb have been associated with changes in regional cerebral blood volume, using a combination of © The Author(s) 2019 This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated Uratani et al Child Adolesc Psychiatry Ment Health (2019) 13:29 positron emission tomography (PET) and NIRS measurements [11, 12] NIRS is a neuroimaging modality that, according to Matsuo et al [13], is especially suitable for psychiatric patients for the following reasons First, because NIRS is relatively insensitive to motion artifacts, it can be used in experiments where motion is expected, such as those involving vocalization Second, NIRS can be used to examine participants while seated in a natural position, with minimal environmental distraction Third, NIRS has cheaper running costs than other neuroimaging modalities and is simple to set up and use Fourth, the high temporal resolution of NIRS is useful for characterizing the time course of prefrontal activity in people with psychiatric disorders [14, 15] Accordingly, NIRS has been used to assess brain function in people with many psychiatric disorders, including schizophrenia, bipolar disorder, depression, obsessive–compulsive disorder, dementia, post traumatic stress disorder, Tourette’s disorder, attention-deficit/hyperactivity disorder, and ASD [13–27] Recent developments in NIRS have enabled noninvasive clarification of brain functions in pediatric psychiatric disorders In pediatric ASD, reduced prefrontal hemodynamic activity has been reported in studies using NIRS measurement during self-face recognition and auditory tasks [28, 29] Yasumura et al [30] reported no significant differences in prefrontal hemodynamic activity between typically developing and ASD children (seven boys and four girls) measured with NIRS during the Stroop task Similarly, Xiao et al [31] reported no significant differences in prefrontal hemodynamic activity between typically developing controls and boys with ASD measured with 16-channel NIRS during the Stroop task However, it is difficult to accurately measure the dorsolateral prefrontal hemodynamic activity using 16-channel NIRS, which is more suitable for measuring hemodynamic responses of the orbitofrontal and frontopolar cortex The Stroop color-word task is one of the most commonly used methods for identifying attentional problems, as well as providing a test of executive function, and involves the dorsolateral prefrontal cortex Moreover, sex differences in executive function in people with ASD have been reported in children and adolescents [32–34] Therefore, it may be valuable to examine the broader prefrontal hemodynamic response in male children with ASD, measured with 24-channel NIRS during the Stroop color-word task We hypothesized that male children with ASD would exhibit reduced prefrontal hemodynamic responses in 24-channel NIRS during the Stroop color-word task Thus, in the present study, we used 24-channel NIRS to examine the characteristics of prefrontal cerebral blood volume changes during the Stroop color-word task in male children with ASD and in Page of 10 age- and intelligence quotient (IQ)-matched healthy control males Methods Participants Twelve drug-naïve male participants, aged 7–15 years, and diagnosed with ASD according to DSM-5 criteria [1], were compared with 12 age- and IQ-matched healthy control males, aged 6–12 years (Table 1) Participants were individuals with ASD who had no history of previous psychiatric disorder treatment, and had consulted one of the experienced pediatric psychiatrists at the Department of Psychiatry of Nara Medical University that anyone with demand could visit at any time without constraints of severity, age, residence, economics, and so on Participants with ASD underwent a standard clinical assessment comprising a psychiatric evaluation, a semi-structured interview system for ASD (the Pervasive Developmental Disorders Assessment System) [35], and an examination of medical history by an experienced pediatric psychiatrist Two experienced pediatric psychiatrists confirmed the diagnosis of ASD in accordance with the DSM-5 Participants’ intellectual level was assessed using the Wechsler Intelligence Scale for Children–Fourth Edition by the psychologist, and individuals with full-scale IQ (FIQ) scores below 70 were excluded Patients who presented with a comorbid psychiatric disorder defined by the DSM-5, a neurological disorder, a head injury, a serious medical condition, or a history of substance abuse/dependence were excluded; two patients with attention-deficit/hyperactivity disorder and two patients with persistent motor tic disorder were excluded Finally, 12 participants with ASD, who had no previous medication history, were enrolled in the present study Of 12 participants, two had been previously Table 1 Participants’ characteristics ASD Control Mean (SD) Mean (SD) Number (sex ratio: M:F) 12 (12:0) Age (years) 9.75 (2.26) First diagnosed age (years) FIQ (WISC-IV) SCWC-1 8.17 (1.95) P value 12 (12:0) 9.50 (2.20) 0.79 NA 100.92 (15.72) 97.83 (7.66) 0.55 34.58 (12.32) 38.58 (7.13) 0.34 SCWC-2 36.92 (10.47) 38.58 (7.96) 0.67 SCWC-3 35.42 (11.98) 37.08 (9.10) 0.71 Group differences tested with t-test ASD autism spectrum disorder, M male, F female, FIQ (WISC-IV) Full-scale IQ score of the Wechsler Intelligence Scale for Children-Fourth Edition, SCWC-1 Stroop color-word task number of correct answers first time, SCWC-2 Stroop color-word task number of correct answers second time, SCWC-3 Stroop color-word task number of correct answers third time Uratani et al Child Adolesc Psychiatry Ment Health (2019) 13:29 diagnosed by the pediatric neurologist at the other hospital, three had been previously diagnosed by using the Autism Diagnostic Interview Revised, one had been previously diagnosed by using the Autism Diagnostic Observation Schedule, and other participants were diagnosed for the first time at the Department of Psychiatry of Nara Medical University Healthy control participants were recruited from local elementary schools and junior high schools They also underwent a standard clinical assessment comprising a psychiatric evaluation, a standard diagnostic interview (Structured Clinical Interview for DSM-IV-TR Axis I Disorders Non-Patient Edition), and an examination of medical history by an experienced pediatric psychiatrist Participants’ intellectual level was assessed using the Wechsler Intelligence Scale for Children-Fourth Edition by the psychologist Finally, 12 healthy control participants, who did not have confirmed ASD and who had no current or past history of psychiatric or neurological disorders, were also enrolled in the present study All participants were able to read the Japanese syllabary characters called hiragana, right-handed and Japanese All participants and/or their parents provided written informed consent for their participation in the study We informed our patients about this study on their initial visit and enrolled them as the participant of this study in order of consent This study was approved by the Institutional Review Board at the Nara Medical University (approval number 325-2) The Stroop color‑word task The traditional Stroop task involves a word-reading task, an incongruent color naming task, and a color naming task We reconstructed the Stroop task according to previously described methods [36] The Stroop colorword task consisted of two pages: each page contained 100 items in five columns of 20 items each and the page size was 210 × 297 mm On the first page, the words RED, GREEN, and BLUE were printed in black ink On the second page, the words RED, GREEN, and BLUE were printed in red, green, or blue ink, with the limitation that the word meaning and ink color never matched The items on both pages were randomly distributed, with the exception that no item could appear directly after the same item within a column Before the task, the examiners gave the participants the following instructions: “This task is to test how quickly you can read the words on the first page, and say the colors of the words on the second page After we say ‘begin’, please read the words in the columns, starting at the top left, and say the words/colors as quickly as you can After you finish reading the words in the first column, go on to the next column, and so on After you have Page of 10 read the words on the first page for 45 s, we will turn the page Please repeat this procedure for the second page.” The entire Stroop color-word task sequence consisted of three cycles of 45-s spent reading the first page, 45-s spent reading the second page (the color-word task) The task ended with 45-s spent reading the first page, which we designated as the baseline task (Fig. 1c) We recorded the number of correct answers in each cycle, and refer to them as follows: Stroop color-word task number of correct answers first time (SCWC-1), second time (SCWC2), and third time (SCWC-3) Examiners who were blind to the participants’ diagnoses administered the Stroop color-word task Importantly, the Stroop task used in this study was different to the traditional Stroop task We used a simplified version of the Stroop color-word task because the participants were school-age children In addition, we excluded the color-naming task (part of the traditional Stroop task) because we needed only two tasks (baseline task and activation task) for our NIRS study The Stroop color-word task was utilized for the following reasons First, the inferior frontal gyrus is reported to be one of the regions most strongly related to Stroop interference [37] Second, in the NIRS study that the same task was used, Negoro et al [26] concluded that suitable prefrontal brain activation in healthy children was recognized by using the Stroop color-word task NIRS measurements Increased oxy-Hb and decreased deoxy-Hb, measured with NIRS, have been reported to reflect cortical activation In animal studies, oxy-Hb is the most sensitive indicator of regional cerebral blood flow because the direction of change in deoxy-Hb is determined by the degree of change in venous blood oxygenation and volume [38] Therefore, we focused on changes in oxy-Hb We measured oxy-Hb using a 24-channel NIRS machine (Hitachi ETG-4000, Hitachi Medical Corporation, Tokyo, Japan) We measured the absorption of two wavelengths of near-infrared light (760 and 840 nm) We analyzed the optical data based on the modified Beer–Lambert Law [39] as previously described [40] This method enabled us to calculate signals reflecting oxy-Hb, deoxy-Hb, and total-Hb signal changes The scale of the hemoglobin quantity is mmol × mm, meaning that all concentration changes depend on the path length of the near-infrared light The recording channels were located over the optical path in the brain between neighboring pairs of emitters and detectors (Fig. 1a) The inter-probe intervals of the system were 3.0 cm, and previous reports have established that the device measures activity at a point 2–3 cm beneath the scalp (i.e., the surface of the cerebral cortex) [19, 41] Uratani et al Child Adolesc Psychiatry Ment Health (2019) 13:29 Page of 10 Fig. 1 Location of the 24 channels of the near-infrared spectroscopy device a Arrangement of emitters and detectors according to the definition of each channel b Corresponding anatomical site of each channel c Timeline of stimulus presentation The baseline task is the word reading task The activation condition is the incongruent color naming task The participants maintained a natural sitting position during NIRS measurements The distance between the eyes of each participant and the paper on which the items were listed was set to between 30 cm and 40 cm The NIRS probes were placed on the scalp over the prefrontal brain regions, and arranged to measure the relative changes in Hb concentration at 24 measurement points that made up an 8 × 8 cm square (Fig. 1a) The lowest probes were positioned along the Fp1–Fp2 line, according to the international 10/20 system commonly used in electroencephalography The probe positions and measurement points on the cerebral cortex were confirmed by overlaying the probe positions on a three-dimensionally reconstructed magnetic resonance imaging scan of the cerebral cortex of a representative participant from the control group (Fig. 1b) The absorption of near-infrared light was measured with a time resolution of 0.1 s The data were analyzed using the “integral mode”: the pretask line was determined as the mean across the 10 s just before the task period; the post-task line was determined as the mean across the 25 s immediately after the task period; using two lines, the baseline was drawn using the least-squares method; the three oxy-Hb changes of the activation task were then averaged The moving average method was used to exclude short-term motion artifacts in the analyzed data (moving average window, 5 s) We attempted to exclude motion artifacts by closely monitoring artifact-evoking body movements, such as neck movements, biting, and blinking (identified as the most influential in a preliminary artifact-evoking study), and by instructing the participants to avoid these movements during the NIRS measurements Examiners were blind to the participants’ diagnoses Statistical analyses We used Student’s t-tests to compare oxy-Hb changes between the two groups by calculating the grand average waveforms every 0.1 s in each channel This Uratani et al Child Adolesc Psychiatry Ment Health (2019) 13:29 analysis enabled more detailed comparison of oxyHb changes along the time course of the task Data analyses were conducted using MATLAB 6.5.2 (Mathworks, Natick, MA, USA) and Topo Signal Processing type-G version 2.05 (Hitachi Medical Corporation, Tokyo, Japan) OT-A4 version 1.63 K (Hitachi Medical Page of 10 Corporation, Tokyo, Japan) was used for the overlap display of the grand average waveforms in both groups in Fig. and was also used to calculate mean oxy-Hb measurements in Table Because we performed 24 paired t-tests, correction for multiple comparisons was conducted using the false discovery rate (FDR) Fig. 2 Grand average waveforms of oxyhemoglobin (oxy-Hb) concentration changes during the Stroop color-word task in both groups The red lines are the grand average waveforms of oxy-Hb in the autism spectrum disorder (ASD) group, and the blue lines are the grand average waveforms of oxy-Hb in the control group The activation task was performed in the time period between the yellow lines Table 2 Correlations between Stroop task and participants’ characteristics ASD SCWC-1 Age FIQ (WISC-IV) Control SCWC-2 SCWC-3 SCWC-1 SCWC-2 SCWC-3 0.790* 0.582* 0.618* 0.577* 0.576* 0.598* − 0.165 − 0.187 − 0.240 − 0.272 − 0.279 − 0.290 Correlations between Stroop task and participants’ characteristics tested with Spearman’s correlation test ASD autism spectrum disorder, FIQ (WISC-IV) Full-scale IQ score of the Wechsler Intelligence Scale for Children-Fourth Edition, SCWC-1 Stroop color-word task number of correct answers first time, SCWC-2 Stroop color-word task number of correct answers second time, SCWC-3 Stroop color-word task number of correct answers third time * P